Arrangement and method for measuring shape of basically two dimensional objects

ABSTRACT

A device and method for measuring geometries or structures of essentially two-dimensional objects involving the use of an image processing sensory mechanism. According to the invention, the object to be measured is placed on an object supporting surface and is measured on the side of the object supporting surface by means of an image processing sensory mechanism that can be displaced underneath the object in a plane running parallel to the object supporting surface.

The invention concerns an arrangement for measuring the shapes orstructures of basically two dimensional objects using an imageprocessing sensor system whereby the object to be measured is arrangedon an object-bearing surface and the image processing sensor system,such as a CCD camera, is arranged on one side of the object.Furthermore, the invention relates to a method for measuring shapes orstructures of a basically two dimensional object using an imageprocessing sensor system, whereby the object to be measured is arrangedon an object-bearing surface and the image processing sensor system,such as a CCD camera, is arranged on one side of the object.

Preferably coordinates measuring devices with an image processing sensorsystem, such as CCD cameras, are used for measuring the shape of chieflytwo dimensional objects such as workpieces or tools, especially for themechanical recording of quality features. These devices are generallyconstructed in such a way that the object to be measured is illuminatedfrom below, moved using a mechanical stage and measured objectstructures of interest are measured in an image processing sensor. Thedisadvantage of the construction principle described consists in thatthe image processing sensor must be refocused when objects havedifferent thicknesses. The refocusing likewise necessary on the objectwhen the smallest height gradations occur delays the measuring sequence.

It is furthermore usual to position the image processing sensor systemfor measuring certain features at the respective location of thefeature, then record and later calculate the workpiece contours. Ageneral overview of the measured object is consequently not obtained.

Furthermore, individual regions of the measured object are brought upseveral times in order to record features lying close to one another.This, likewise, leads to lengthening the measuring time.

So-called scanner systems are also known where greater sections of aregion can be scanned with line-like sensors. The disadvantage of suchsystems lies in that the image information from a linear scanning motionin one direction and the sensor shape in a second direction are joinedtogether. The particular shape of the sensor system likewise requiresimaging optical systems that basically do not permit a high gradeimaging. In the end, the measuring devices manufactured according tothis principle are outfitted with only a low exactitude.

The present invention is based on the problem of developing further anarrangement and a method of the type mentioned at the beginning in sucha way that two-dimensional objects or their shapes, especially objectedges and corners and margins, can be measured very rapidly with highaccuracy.

To solve the problem, it is basically provided in accordance with thearrangement that the image processing sensor system is located beneaththe object and can be adjusted on a plane running parallel to theobject-bearing surface.

In particular, the mobile image processing sensor system is arranged ina closed housing that is closed off on the object side by a transparentsurface on which the object can be positioned. Obviously there alsoexists the possibility of arranging the object on a separate objecttable at a distance from the transparent surface.

In a further development, the invention provides that an illuminationapparatus is arranged above the object or workpiece bearing surface,preferably as a luminous surface.

It is in particular provided that the arrangement includes housing witha closed lower part and a roof. The closed lower part includes thesensor unit with optical unit as well as a drive and is provided with atransparent covering, such as a glass plate on which the object to bemeasured can be positioned. The cover itself has the illuminationapparatus, whereby a measurement can only take place when the covermasks the lower part of the housing, thus closing it off Consequently,the object is surrounded on the peripheral side completely by thehousing during measuring, thus by the housing and the cover, so that anunintended dislocation of the object or other change influencing themeasurement cannot take place.

Additionally, it can be provided that the object is surrounded by lightsources beaming in the direction of the object, such as light diodes, inorder to illuminate the object on the sensor side.

A telecentric objective with a great depth of field can be used as animaging optical system for the image processing sensor unit. The depthof field can, for example, come to 50 mm without a restriction takingplace through this.

The position of the image processing sensor unit can be adjusted withthis allocated XY drive, whereby the position is measurable throughcorresponding scale systems.

An image memory can be connected as an image processing sensor thatrepresents the size of a desired, especially overall measuring range ofthe device. Furthermore, an evaluation computer unit can be allocated tothe image memory for the measuring range, especially overall measuringrange, that undertakes the geometric evaluation on the overall imagecontent.

Preferably the image processing sensor system includes matrix-like imageprocessing sensors and is constructed as a CCD matrix camera.

A method for measuring shapes of basically two-dimensional objects ofthe type mentioned at the beginning is distinguished in that the imageprocessing sensor system is arranged adjustably on a plane beneath theobject-bearing surface that runs parallel to the object-bearing surface.

Accordingly, an image processing sensor with an upward direction of viewis arranged mobile on a plane beneath the measured object.

Moreover, images can be recorded on several positions of the measuringregion using the image processing sensor system and these can becompiled into an overall image by computer in the image memory. Therealso exists the possibility of recording images separately over theentire measuring region and joining these together into an overallimage. Moreover, the overall image can be evaluated with respect togeometric features with an image processing system. For example, thefield of vision of the sensor can come to 50×80 mm² and the measuringregion to 400×200 mm to name some figures only by way of example.

The theory of the invention makes it possible to reduce or avoid thedisadvantages immanent in the state of the art. This takes place inaccordance with the invention in that the moved image processing sensorsystem is arranged beneath the object and for example beneath a glassplace with a direction of view on the object, hence upward. This leadsto the fact that the measuring object regions and edges of the measuredobjects can respectively come to lie on the same plane independently ofthickness. Focusing the sensor unit is consequently not necessary.

Furthermore, the inventive use of an optical system with sufficientdepth of field makes possible measuring even graduated objects in oneplace without a focusing process.

To optimize measuring time, the entire measuring field or sections ofthe measuring field can be selectively scanned by lining up positions ofthe image processing sensor unit. An overall image is virtuallygenerated in the adjoining image processing computer. The metrologicalevaluation takes place in the overall image in a single operation.Consequently, positioning procedures are spared and a general overviewover the object to be measured is obtained.

Even sections of the measuring field can be represented as a partialoverall image and then evaluated in an image processing system.

The disadvantages of the state of the art are in particular avoided bythe exact positioning of matrix-like image processing sensors.

It is preferably provided that an optical system with variable workdistance is used for recording the object or regions of the latter.Nonetheless, in particular an optical system that has a zoom opticalsystem can be used that contains at least two lens groups that arerespectively axially displaceable separately by a motor. Refer to thisextent to WO 99/53268 to the disclosure of which reference is explicitlymade.

It is proposed in a refinement of the invention that first a crudealigning of the image processing sensor on the position of the object orpart of the object to be measured takes place, whereby when aligning theimage processing sensor, the latter is moved with an acceleration a₁>0mm/s², in order then to brake the image processing sensor and to measurethe position when the image processing sensor is moved at anacceleration a₂ with 0 mm s₂≦a₂<a₁. If need be, the object can moreoveradditionally be energized with a light flash, or a CCD camera withshutter can be used as the image processing center. A correlationbetween the motion of the sensor and the image to be respectivelyrecorded takes place through measures in this regard, whereby anapparent stoppage of the image processing sensor is realized through thelight flash or the shutter with the consequence that measurements areconducted such as if the image processing sensor would stand stillduring the measurement.

Further details, advantages and features of the invention emerge notonly from the claims, the features to be inferred from these-bythemselves and/or in combination, but also on the basis of the followingdescription of preferred designs to be inferred from the drawing,wherein:

FIG. 1 illustrates a basic representation of an arrangement formeasuring a two-dimensional object,

FIG. 2 a +2 b illustrates a basic representation of a first design of ameasurement method and

FIG. 3 a +3 b illustrates a basic representation of a second design of ameasurement method.

In FIG. 1, an arrangement for measuring an essentially two dimensionalobject 10 is very basically that is arranged on an object-bearingsurface 12. This is constructed transparently and in particular as aglass plate in accordance with the invention in order to be able tomeasure the object 10 from underneath. An image processing sensor system14 is arranged adjustable in the X and Y direction of a coordinatesmeasuring device beneath the object-bearing surface. The imageprocessing sensor system consists preferably of a CCD matrix camera 16in front of which an optical system 18 is arranged, especially in theform of a telecentric objective.

Moreover, the object-bearing surface 12 can be the surface of a housingin which the image processing sensor system 14 can be adjusted in the Xand Y direction in relation to the object 10. The housing surface ismoreover transparent, whereby the object 10 either lies directly on thehousing surface or at an equidistant spacing toward the latter.

Due to the fact that the moved image processing sensor system 14 isarranged beneath the object 10 and beneath the object-bearing surface 12particularly constructed as a glass plate with a direction of view tothe object 10, a focusing of the sensor system 16 is no longer necessarywith a sufficient depth of field of the object 18 since the objectregions to be measured come to lie in the same plane as edges ofboreholes 20 in the design independently of the thickness of the object10, namely on the object-bearing surface 12 which has a constantdistance independent from the position of the image processing sensorsystem 14 in relation to the latter.

If the objective 10 is arranged directly upon a glass plate in thedesign, then obviously there also exists the possibility of arrangingthe object 10 spaced toward this, but at an equidistant spacing.

An illumination, especially in the form of a flat light field 22, isprovided for illuminating the object above this, thus on the side of theobject 10 lying opposite the image processing sensor system 14.

The flat light field should moreover be incorporated into a cover thatcloses the housing in which the image processing sensor system 14 isarranged with the optical system 18 and the drive and which is closedoff by a transparent element such as a glass plate in reference to thefield of illumination side on which the object to be measured can bepositioned. Moreover, usually a measurement should only be conductedwhen the cover containing the light field 22 completely covers thehousing, thus closes it on the glass plate side.

In order to conduct precise measurements with great speed, it isprovided in accordance with the invention that the image processingsensor system 14 records images at several positions 24, 26, 28, 30, 32,34, 36, 38 of the object 10 to be measured, which basically correspondto the respective field of sight 25, 37 in FIGS. 2 a and 3 a in theimage processing sensor system, and which are represented by squaresframed by dotted lines, in order then to join the respective images intoan overall image according to FIG. 3 b by computer in an image memory inaccordance with FIG. 2 b, or in the case of imaged recorded separately(FIG. 3 a). Geometric features such as position of a measuring site 44,46 or distance 48, 50 of measuring points or measuring sites can the beevaluated on the basis of the respective overall image 40 or 42. Thefield of vision 24, 25, 26, 28, 30, 32, 34, 36, 37, 38 can, for example,amount to a size of 50×80 mm² and the measuring region to 400×200 mmwithout this being understood as restrictive.

In other words, the entire field of measurement (FIG. 2 a) or sectionsof the field of measurement (FIG. 3 a) can be selectively screened bylining up positions of the image processing sensor such as the matrixCCD camera 16 for optimizing measurement time in accordance with theinvention. On the basis of this, an overall image 40, 42 is generatedvirtually in a connected image processing computer, whereby themetrological evaluation takes place in the overall image in a singleoperation. Consequently positioning processes are spared and an overalloverview on the object 10 to be measured is obtained. The disadvantagesof the state of the art are avoided through these measures by exactpositioning of matrix-like image processing sensors.

Independently of this, the measurement process can be optimized in thatfirst of all a crude aligning of the image processing sensor on theobject to be measured takes place, whereby the image processing sensoris moved with an acceleration a₂>0 mm/s² when aligning the imageprocessing sensor and the position is measured when the image processingsensor is moved at an acceleration a₂ with 0 mm/s²≦a₂<a₁. Moreover, animage processing sensor in the form of a CCD camera with shutter can beused, due to which the advantage results that an apparent stoppage ofthe image takes place during measurement regardless of the motion of thesensor. The same can be realized with a light flash.

In other words, the image processing sensor only moves crudely on theposition to be measured and is then measured when the image processingsensor is moved further, but basically not accelerated. For measurement,it can be moved with a speed of v₁ of, for example 50 to 200 mm/s.Moreover the image storage necessary for measuring can be recognized inthe image processing sensor by reaching a target area. Braking can thusbe introduced by optical recording of the area of the object containingthe position using the image processing sensor.

Moreover, a motion of the image processing sensor can take place in sucha way that at a speed of vi, the object or measuring region or measuringpoints of the latter are measured, and the image processing sensor issubsequently strongly accelerated, for example, to a value of ca. 5000to 15,000 mm/s in order then to be crudely aligned at an acceleration of0 mm/s² at a speed v₂ between 400 and 600 mm/s on the measuring regionor measuring point. Then a braking of the image processing sensor tospeed v₁ takes place in the range preferably between 50 mm/s and 150mm/s in order to perform measurements. During this time the object orthe region to be measured can be activated by light flashes or theshutter of the image processing sensor can be opened and closed at thedesired frequency. After measurement has taken place, the imageprocessing sensor is then accelerated in the direction previouslydescribed in order to be aligned on a new measuring point or region.

1. Arrangement for measuring shapes or structures of basically twodimensional objects (10) by means of an image processing sensor system(14), whereby the object to be measured is arranged on an object-bearingsurface (12) and the image processing sensor, such as a CCD camera (16),is arranged on one side of the objects, wherein the image processingsensor system (14) is arranged beneath the object (10) and is adjustableon a plane running parallel to the object-bearing surface (12). 2.Arrangement according to claim 1, wherein the image processing sensorsystem (14) includes matrix-like image processing sensors, especially aCCD matrix camera (16).
 3. Arrangement according to claim 1, wherein theimage processing sensor system that is movable in the X and Y directionof a coordinates measuring device is arranged in a closed housing thatis transparent or translucent on the object side and the object-bearingsurface (12) is or runs parallel to the object-bearing surface. 4.Arrangement according to claim 1, wherein an illumination apparatus(22), preferably in the form of a luminous surface, is arranged abovethe object to be measured or the object-bearing surface (12). 5.Arrangement according to claim 4, wherein the illumination apparatus(22) is incorporated into a cover closing the housing on theobject-bearing surface side.
 6. Arrangement according to claim 1,wherein the imaging optical system (18) of the image processing sensorysystem (14) is a telecentric objective with great depth of field. 7.Arrangement according to claim 6, wherein the imaging optical system(18) is surrounded, preferably concentrically, by illumination elementssuch as light diodes for illumination of the image processing sensorside surface of the object (10).
 8. Arrangement according to claim 1,wherein the position of the image processing sensor system (16) isadjustable with this allocated x-y drive and the position is measurablethrough corresponding scale systems.
 9. Arrangement according to claim1, wherein an image memory is connected to the image processing sensor(16) that represents the magnitude of a desired measuring region (40,42), especially the overall measuring region of the arrangement. 10.Arrangement according to claim 9, wherein an evaluation computer unit isallocated to the image memory (40, 42) for the measurement region whichundertakes the geometrical evaluation on the overall image content. 11.Method for measuring shapes or structures of a basically two dimensionalobject using an image processing sensor system (14) whereby the objectto be measured is arranged on an object-bearing surface (12) and the Nimage processing sensor system such as a CD camera (16) is arranged onone side of the object, wherein the image processing sensor (14) isarranged beneath the object-bearing surface (12) and is adjustable on aplane which runs parallel to the object-bearing surface.
 12. Methodaccording to claim 11, wherein the image processing sensor system (14)moves in the X and Y direction of a coordinates system and is arrangedin a stationary closed housing that is closed off on the object side bya transparent surface on which the object (10) is laid or toward whichthe object is arranged at a distance on a plane running parallel to thesurface.
 13. Method according to claim 11, wherein an illuminationapparatus (22), preferably in the form of a luminous surface, isarranged above the object-bearing surface (12) or the object to bemeasured (10).
 14. Method according to claim 13, wherein theillumination apparatus (22) is incorporated into a cover through whichthe housing can be masked, whereby a measurement of the object (10) isprevented when the cover exposes the object-bearing surface (12). 15.Method according to claim 11, wherein a telecentric objective with greatdepth of field is used as an imaging optical system (18) of the imageprocessing sensor (16).
 16. Method according to claim 11, wherein theposition of the image processing sensor (16) is adjusted with thisallocated x-y drive and the position is measured by appropriate scalesystems.
 17. Method according to claim 11, wherein an image memory isconnected to the image processing sensor (14) that represents themagnitude of a desired or overall measuring region (40, 42) of thearrangement.
 18. Method according to claim 17, wherein an evaluationcomputer unit is allocated to the image memory for the desired oroverall measuring region (40, 42) which undertakes the geometricevaluation on in particular the entire image content.
 19. Methodaccording to claim 11, wherein images are recorded at several positions(24, 26, 28, 30, 32, 34, 36, 38) using the image processing sensorsystem (14) and these are assembled by computer in the image memory intoan overall image (40, 42).
 20. Method according to claim 11, whereinimages (24, 26, 28, 30, 32, 34, 36, 38) are recorded that aredistributed over the entire measuring region and they are joinedtogether into an overall measurement image (40, 42).
 21. Methodaccording to claim 11, wherein the overall image (40, 42) is evaluatedwith respect to geometrical features with an image processing system.22. Method according to claim 11, wherein the following operations areconducted for measuring the object (10) or a region thereof: crudealigning of the image processing sensor (14) on positions of the object(10) to be measured, whereby when aligning the image processing sensor,this is moved with an acceleration a₁>0 mm/s², and braking the imageprocessing sensor in measuring position when the image processing sensoris moved at an acceleration a₂ with 0 mm/s²≦a₂<a₁.
 23. Method accordingto claim 22, wherein the object (10) is acted upon with a light flashduring measurement or a CCD camera with shutter is used as an imageprocessing sensor (16).
 24. Method according to claim 15, wherein animaging optical system with variable working distance, especially animaging optical system with a zoom optical system, is used that containsat least two respective lens groups axially and separately displaceableby a motor.